1. Field of the Invention
This present invention relates generally to the field of electronic circuitry and, more specifically, to forming diodes.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In today's high-speed computer systems, the relative size of electronic devices is steadily decreasing as technology advances. Generally, the reduction in the overall footprint of the electronic components is due to the consumer's demand for smaller, more powerful electronic devices. The different components of an electronic system generate signals that are transmitted from one component to another. For example, processors transmit signals to associated memory devices to read and write data. As the size of these electronic devices becomes smaller, the magnitude of the electrical signals they use also decreases. This decrease is not only due to the inability of smaller electronic structures to handle large electrical signals, but also due to the desire to produce electronic components that consume less power and generate less heat.
The signals from one electrical component to another are typically digital signals, in that they indicate a “logical 0” state or a “logical 1” state. The “logical 0” state is usually a zero voltage state, and the “logical 1” state is a steady voltage state. In transitioning from the zero voltage state to the steady voltage state, the voltage and current may oscillate at levels above and below the steady voltage state until a constant steady voltage state is achieved. One issue faced by the designers of the electronic systems is protecting the various components from damage as a result if peaks in the oscillations of the overvoltage or over-current situations.
Historically, memory devices have used a voltage clamp between the input pad of the device and the internal circuitry to prevent the over-current or over-voltage situation from damaging the memory device. Generally, the voltage clamp includes a pair of MOSFET diode connected transistors in series. A limitation with the MOSFET diode-connected transistors is that the forward bias current handling capacity is limited by a squared function. As technology advances, it is generally desirable to scale down the size of all transistors on an integrated circuit, because such scaling simplifies the design process, saves valuable chip space, and facilitates efficient manufacturing.
However, the current handling capacity of the smaller MOSFET diode-connected transistors raises some concerns for designers. While the larger MOSFET diode-connected transistors are able to handle the over-voltages and over-currents of the input signals, the smaller MOSFET diode-connected transistors may be unable to do so. In other words, the reduction in the size of the MOSFET diode-connected transistors limits their effectiveness in a voltage clamp. As a result, the MOSFET diode-connected transistors used in voltage clamps remain relatively large and cannot be scaled down with the other transistors in the memory device.
Diodes may be used in place of MOSFET diode-connected transistors because diodes exhibit a greater current carrying capacity for a given size. To manufacture these diodes, a fabrication process typically uses a P well or an N well in conjunction with an N+ doped silicon or P+ doped silicon, respectively. Generally, the interface between the doped region and the well covers a large surface area and is not optimally defined. Also, the P well or the N well may not be adequately isolated. If a well is not adequately isolated, then too many carriers may be injected into the substrate and degrade performance. With the current flow above the specified parameters for a circuit, a state of latch-up may occur. Once latch-up occurs, the circuit output may become fixed and not react to input signals.